The present invention relates to communication devices in general and portable units with an electro-acoustic converter in particular.
In a conversation between two partners A and C over a communication system (e.g., telephone, radio) both partners A and C must be able to understand each other acoustically. There are conversation situations where a further person B is situated near to A.
In a first case, person B is excluded at least in part from the conversation when C is speaking about matters which concern A but not B. B can hear A but should not be able to hear C. In a second case, B is invited to take part in the conversation and listens to A as well as to C.
The system terminal device on the side of persons A and B is (i) in the first case set to modus QUIET (the speaker at A""s ear is set to a low volume) and (ii) in the second case is set to modus LOUD (a high volume which both A and B can hear).
A portable personal communication device is known from patent number EP 0564 160 B1 (Bowen et al, German translation DE 693 18 613 T2) which can work both in earpiece mode with an ear coupling and in open loudspeaker mode or loud telephone type device mode, switching automatically between the two modes based on a continuous measurement of the distance between the listener and audio output unit. This document also further justifies the need for both modes of operation.
A portable radio is known from JP 9162772 A (Suzuki et al), in which during operation an infrared sensor determines the distance between user and radio and sets the speaker volume level as a function of this distance. The setting of the volume also serves, for example, to protect the listener from excessively high volumes.
The switch-over between the operating modes is determined according to the distance head-to-device, and thus the space therebetween. Environmental influences (for example, changing dielectric constants, further infrared sources) could effect the mode change.
There is a task of the invention to design a communication device which avoids that disadvantage.